Ultrasonic pulse echo rangefinding is used to detect nearby objects. Ultrasonic pulse-echo measurements bounce sound off the object and measure the time-of-flight (ToF) of the echo. The ToF can be converted into round-trip range by multiplying by the speed of sound.
If several ultrasonic transceivers are used at specific locations in space, the position of a nearby object can be determined in 2 or 3 dimensions. Using this technique, an input device can be constructed to track the location of a user's finger, for example. The position or motions of the finger can be used as a primary or alternative input mechanism for devices such as phones or wearables. Often, the same transceiver is used to transmit ultrasonic pulses and detect return echoes of those pulses. If an object is located near an ultrasonic transceiver, a transmitted ultrasonic pulse and a return echo from the object may interfere with each other. Such interference can prevent accurate ToF measurement and tracking for objects that are close to the transceiver.
It is within this context that aspects of the present disclosure arise.